An Organic Light Emitting Diode (OLED) is an organic thin film electroluminescent (EL) device, which has advantages of simple fabrication process, low cost, high luminous efficiency and easy formation of flexible structure. Therefore, display technology employing an OLED has become important display technology.
An OLED display device comprises a plurality of pixel units, each of which has an OLED disposed therein. The luminous intensity of each OLED is controlled by controlling current flowing through the OLED, thereby realizing image display. Herein, each visible pixel on a display is made of a plurality of adjacent pixel units emitting light of different colors, and light emitted from the respective pixel units is mixed to form light emitted from the visible pixel. Colors (that is, colors of the corresponding color filter films) of the pixel units constituting the visible pixel may be selected in different modes, such as the RGB (red, green, blue) mode (that is, a red pixel unit, a green pixel unit, and a blue pixel unit form a visible pixel unit), the RGBW (red, green, blue, white) mode and the RGBY (red, green, blue, yellow) and the like.
As technologies of white OLEDs (WOLEDs) are well developed and WOLEDs have high luminous efficiency, the OLEDs are widely used in OLED display devices.
As illustrated in FIG. 1, a visible pixel unit of a WOLED display device may comprise three pixel units 9R, 9G and 9B of red, green, and blue (Of course, other modes are also applicable) disposed on a substrate 7, each pixel unit 9R, 9G or 9B has a Thin Film Transistor (TFT) drive layer 1 disposed therein, and an anode (a first electrode 21), a light emitting layer 23, a cathode (a second electrode 22), an encapsulation layer 8, and a color filter film 3R, 3G, or 3B (also referred to as a color filter plate) with a corresponding color are sequentially disposed on the TFT drive layer 1. The anode, the light emitting layer 23 and the cathode form an OLED 2. The TFT drive layer 1 may drive the anodes of the respective pixel units 9R, 9G and 9B independently, such that the respective OLEDs 2 emit light with different brightness, which becomes light of different colors after passing through corresponding color filter films 3R, 3G and 3B and is then mixed to form light emitted from the visible pixel.
To improve luminous efficiency, a microcavity structure may be formed in an OLED display device. The microcavity structure is a structure with a thickness in micron dimension formed between a reflection layer and a transflective layer and light is continuously reflected between the two layers. Due to the resonance effect, light with specific wavelength in the light eventually emitted from the transflective layer is enhanced, and the wavelength of the enhanced light depends on the thickness of the microcavity structure.
In a WOLED display device, different pixel units are used to emit light of different colors. Therefore, microcavity structures at different pixel units should enhance light with different wavelengths (light having the same color as the color filter film), that is, the microcavity structures at different pixel units are of different thicknesses. To achieve this, as illustrated in FIG. 2, in the WOLED display device, the cathode is set as a transflective layer 6, the anode is set as a transparent layer, and a reflection layer 4 is further disposed blow the anode. As such, the thicknesses of the microcavity structures of the corresponding pixel units 9R, 9G and 9B may be controlled by adjusting the thicknesses of respective anodes.
However, the inventors find that at least the following problem exists in the prior art: the respective anodes of the array substrate are disposed in the same layer and may be originally formed in a single patterning process at the same time. However, in a WOLED display device having microcavity structures, the anodes of respective pixel units are of different thicknesses, and therefore they are separately formed in a plurality of patterning processes, or a dual-tone mask needs to be used in the patterning process, while these methods lead to complicated fabrication process and high cost.